| Current Conditions | ||
| Temp |  | 3.7 C |
| RH | | 74 % |
| Wind | | WSW 18 mph |
| Road | | Open (4x4) |
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Hawaiian Islands Synoptic Discussion and Guidance 220 FXHW60 PHFO 220156 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 356 PM HST Thu Sep 21 2017 .SYNOPSIS... Locally breezy trades will gradually weaken during the next couple of days as surface high pressure far northeast of the state erodes. A typical pattern of mainly windward showers will prevail, though interior and leeward Big Island will experience extensive afternoon cloud cover and a few showers through at least the weekend. && .DISCUSSION... A locally breezy and mainly stable trade wind flow persists this afternoon. The trades are being driven by a somewhat strong 1033 mb high sitting 1600 miles northeast of the islands and its associated ridge stretching about 650 miles north of Kauai. A trough within the ITCZ remains north of 10N, and this is helping to enhance the winds as the pressure gradient over the state is somewhat tight. Mid level ridging is producing an inversion between 6,000 to 7,000 ft according to the afternoon soundings and aircraft data, and precipitable water within the trade wind flow ranges from near September normal of almost 1.5 inches to as low as 1.1 inches in dry slots. The result has been modest rainfall along mainly windward slopes. The far southwestern edge of an upper level trough remains over the islands. This feature is having little effect other than pulling up some elevated moisture near the Big Island. Expect little change tonight. Locally breezy trade winds will ease slightly, and modest shower activity will be focused over windward slopes. Clouds and a few showers over leeward Big Island will clear as nighttime land breezes kick in. A gradual decrease in trade winds is due on Friday and Saturday as the ridge currently 650 miles north of the state is pushed southward. Moderate trade winds are forecast to persist through the upcoming week. No big changes in the moisture content and stability of the trade wind flow are noted in the near future. As a result, showers will continue to be largely confined to windward slopes. The upper level trough will meander in place through the weekend, which will likely lead to continued afternoon cloud cover and spotty showers over leeward and interior Big Island. && .AVIATION... VFR conditions prevail at all TAF sites and these conditions are expected to continue this evening and on through the overnight hours. There will likely be some brief MVFR conditions along windward slopes at times as moisture riding in on the trades interacts with island terrain. AIRMET Tango remains in effect for low level turbulence over and immediately south and west mountain ranges of all islands. The AIRMET is expected to continue through the overnight hours and possibly through the day Friday. && .MARINE... Fresh to locally strong trades will continue tonight driven by a 1032 mb high pressure far north-northeast of Hawaii. Trades should gradually weaken over the next couple of days to the light to moderate range by the end of the weekend. This pattern should hold through the first half of the upcoming week. Before they weaken, the trade winds will bring rough surf along east facing shores. In the far southern offshore waters, thunderstorms will occur along a trough along the Intertropical Convergence Zone tonight, moving west of the offshore area by Friday. Surf along south facing shores will remain small through early next week with mainly background southeast and southwest swell energy expected. The next potential long-period pulse out of the southwest from the Tasman Sea will be possible by Sunday, which should lead to a slight increase in surf. For the extended, strong to gale-force southwest winds associated with a low that has been impacting the Tasman Sea may lead to another small southwest (210-220 deg) swell Tuesday through midweek. A small northwest (310 deg) swell will continue into the weekend before easing. Another small reinforcement is due is expected to fill in around Sunday night through middle of next week. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 AM HST Friday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ Public...Wroe Aviation...Burke Marine...Foster Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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